1. Field of the Invention
The present invention relates to a friction grip hoist for handling loads.
2. Description of the Related Art
More particularly, the invention relates to a hoist comprising: at least one body; a sheave or pulley mounted on said body, said pulley comprising a pin and a wheel engaged on said pin, said wheel, referred to as a “grooved” wheel, being provided with an outer peripheral groove for receiving a cable; drive means for driving rotation of said wheel; and holder means suitable for exerting a thrust force towards the bottom of the groove of the wheel in order to hold the cable inside the groove of the wheel by pressing thereagainst.
One such hoist is known from U.S. Pat. No. 4,005,852.
Friction grip hoists should not be confused with drum hoists or jaw hoists. Friction grip hoists present the characteristic of being suitable for use with a cable of great length on the basis of the cable being held by gripping inside a single groove of the pulley, the width of the groove corresponding substantially to the diameter of the cable that is to be received in the groove, such that the cable presents only one turn wound around said pulley.
Such friction grip hoists are used in particular for accessing the outsides of buildings, for accessing work zones in elevator shafts, in wells, in silos, ( . . . ). Compared with other hoists they present the following advantages:                no limit on height; and        the hoist can accompany the load.        
Until now, in order to avoid overloading the hoist and in order to guarantee that the hoist stops operating on exceeding the theoretical capacity of the hoist, a friction grip hoist presents at least one force sensor in its zone where it is fastened to the equipment fitted with the hoist. This force sensor may for example be in the form of a spring arranged in the zone where the hoist is fastened to the equipment fitted with the hoist.
There are numerous drawbacks in such a solution:                the measurement means for avoiding an overload are dedicated to the fitted hoist;        the measurement means for avoiding an overload require predetermined fastening of the hoist to the equipment that is fitted with the hoist; and        the measurement means for avoiding an overload are generally very sensitive, and as a result they are difficult to adjust and lack accuracy.        